Disclaimer: the people and events are, I believe, held in joint contract by Shakespeare and history. Creatively speaking, Cantorculus is mine, although given the way these things work, his real-life pseudo-predecessor probably owned me.
Cassius had not intended to impart whisperings of dissent to Brutus - neither his discontent with Caesar's rule nor the ideas of revolt that even to him were still little more than hints. His purpose was very much to attend and lose himself in the festivities of the Lupercal, or at least in the company of a friend, secured against the chance that Cassius might fall too far into the seething mass of mindless followers. He did not wish for his own company and most certainly did not wish to be at home, where there was no longer a Cantorculus prowling about through the rooms or asleep in a sunny place in the garden.
The cat had passed away sometime in the night and been discovered by one of the slaves in the morning, curled up in a storage room. Someone had brought word to Cassius, and he had gone in a rush to see the little creature once more, shedding a half-donned toga in the flurry. He had knelt beside it, stroked its ears and the short fur of its back a final time, and given orders that the body be buried in some corner of the garden. He did not deceive himself that the creature had been at all human, but Cantorculus had gone about his business with purpose and efficiency, which was more than could be said of many men, and there had been pleasant interludes when man and cat alike had set aside their respective labours to humour one another. Cassius could not bar to think of the corpse thrown into the street gutter with all the other offal of the household and the rest of the city.
He had departed the house as soon as he could thereafter, clad at last in a fresh toga, and set off through the streets to find whomever he should happen to meet, or else the great crowds celebrating the holiday, if no one of particular interest should present himself. The streets were thronged all about, though not until he had manoeuvred his way to the centre of the revels did he find anyone with whom he was at all inclined to do more than exchange a brief greeting. As he went, he had passed one street that looked more like the day after a festival rather than the day of. It had been deserted and bare of adornment, save for a few trampled garlands, but he gave it no thought except to turn his back on it: it was too much like the Cantorculus-less house he had left in such haste.
At the heart of the festivities he found Cicero and Casca, which was promising, and Caesar and Antony, who were, at least, diverting. There was also some mad prophesier who was irksome and, worst of all, situated near to Cassius in the crowd. The ceremony and interruption alike dispensed with, Caesar and the crowd continued on to view the race, but Cassius glimpsed Brutus winding his way out of the throng and away from the course. In that moment, the company of one Marcus Brutus was the most essential salve to Cassius' misery.
They had not spoken for several weeks, but never mind whose fault their estrangement had originally been, Cassius was going to end it and drag this man, again a friend, to the festivities. Cassius had expected that he would have to be coercive, but Brutus' short answers had stung him to speak more accusingly of Brutus' actions than he had intended. Perhaps, though, Brutus had wished as much as Cassius to end their alienation, for he apologized freely.
He admitted that he numbered Cassius among his friends.
By the time he had finished, the street had altogether emptied, and the Lupercal race had lost whatever inexplicable appeal it had previously held. No, Cassius had not planned to seduce Brutus into his half-formed schemes against Caesar, not just yet, but now that Cassius had Brutus to himself, he needed to keep him with some conversation, and the opportunity to give vent at last to his disgust with Caesar and the Rome he had created was too propitious to let pass. It was, in fact, exactly the moment he had been waiting for; Cassius took it.
Not until Brutus spoke of wishing to take his leave of Cassius, and a decidedly un-festive procession of spectators returned from the race, did Cassius recall his pressing desire for company of any sort and the reason for that urge. Casca provided some further diversion, and Cassius endeavoured to detain him as long as was possible. Unhappily, the self-professed ignoramus of Greek showed himself remarkably . . . cat-like, for want of a better word - Cassius was sure that Casca's claim of a prior engagement for the evening was as false as his sudden linguistic deficiency. Though he secured Casca's companionship for dinner the following day, Cassius was to be left with only himself for the present night.
No! Not quite himself: there was still his plot - just beginning to take shape - and Brutus still to be fully convinced. A night spent in forging letters and finding opportunities to place them in Brutus' way would see him through to the next day, at the least. After that . . . well, something else would come.